select_vars: Selective use of default "$PWD/pki/vars"

If either EASYRSA or EASYRSA_PKI is already defined when searching for
default "$PWD/pki/var" then ignore this default vars file.

If EASYRSA_PKI is defined then do not load a vars file from a different PKI.
If EASYRSA is defined then do not load a vars file from any PKI.

Signed-off-by: Richard T Bonhomme <tincantech@protonmail.com>

easyrsa3/easyrsa

@@ -5642,7 +5642,10 @@ select_vars() {
 		fi
 
 		# Default PKI; if vars exists, use it ONLY
-		if [ -e "$PWD/pki/vars" ]; then
+		if [ -e "$PWD/pki/vars" ] && \
+			[ -z "$EASYRSA_PKI" ] && \
+			[ -z "$EASYRSA" ]
+		then
 			# Prevent vars from changing expected PKI.
 			# A vars in the PKI MUST always imply EASYRSA_PKI
 			# This is NOT backward compatible